In recent years, products on which an illuminance sensor is mounted have been increased for the purpose of adjusting display brightness or the like in mobile phones, liquid-crystal television sets, and the like. In the illuminance sensor, sensitivity equal to the sensitivity of human eyes is required. However, an optical semiconductor light-receiving element to be used for the illuminance sensor has sensitivity toward not only visible light but also a near-infrared light region of about 800 to 1100 nm and thus perceives near-infrared light, which is imperceptible by human eyes, as it is. As a result, there arises a problem that the sensor falsely judges “bright”.
In order to prevent the occurrence of such a problem of the illuminance sensor, for example, it is necessary to block the sensitivity of the optical semiconductor light-receiving element toward the near-infrared light by providing an optical filter or the like on the optical semiconductor light-receiving element. On the other hand, as an encapsulating material for the optical semiconductor light-receiving element, epoxy resin compositions having excellent heat resistance, impact resistance, transparency, and the like have been hitherto widely used.
Thus, in the illuminance sensor as above, for example, there have been performed a method of providing two kinds of optical semiconductor elements different in peak wavelength of light-receiving sensitivity and calculating visible light components based on the difference in light-receiving sensitivity of both elements to compose an illuminance sensor and a method of coating the light-receiving upper surface of the sensor with an optical filter material having a near-infrared light-blocking function and encapsulating the optical filter in the formed state with an epoxy resin composition transparent over a visible light region and a near-infrared light region to form an illuminance sensor (see JP-A-2004-6694).